1. Field of the Invention
The invention relates to a control unit of a motor vehicle having a plurality of control elements arranged in a visible surface of the control unit, at least one of which elements can be illuminated by a light source via a light coupling-out area of an annular optical waveguide. Furthermore, the invention relates to a control unit of a motor vehicle having a plurality of control elements arranged in a visible surface of the control unit, which elements can be illuminated by a light source via light coupling-out areas of an optical waveguide.
2. Description of the Related Art
Control units of a motor vehicle, such as e.g. those for an air-conditioning system or a navigation system, have a plurality of control elements. In order to ensure reliable control of the control units even at night, the control elements must be able to be reliably recognized even when it is dark. The control elements can be visually identified e.g. by the control element itself containing a luminous marking or, alternatively, by a luminous ring being arranged around the control element. Since the space behind the control element in the control unit is generally occupied by the component actuated by the control element, such as e.g. a potentiometer, use is often made of optical waveguides which guide the light from a light source to the desired location in the control unit. At the same time, it is also necessary to ensure uniform illumination.
The light sources used are generally a plurality of light-emitting diodes which are arranged on a printed circuit board in the control unit and whose light emission takes place perpendicularly to the plane of the printed circuit board. Although the emission from the light-emitting diodes takes place, in principle, in the direction of the visible control surface of the control unit, the light-emitting diodes cannot be arranged directly behind the element to be illuminated, for the reasons mentioned above. Moreover, such a direct arrangement of the light-emitting diodes, e.g. in the case of the illumination of a control element by means of luminous rings would also lead to non-uniform light distribution. For this reason, too, the light emitted by the light-emitting diodes is coupled into an optical waveguide and guided via the latter to the desired location. In order to keep the loss of light low in this case, it is necessary to adhere to sufficiently large radii of the optical waveguide for light deflection. This results in correspondingly large installation depths of the control unit.
FIG. 6 illustrates such a known arrangement according to the prior art. A control element 63 is arranged in a visible front face 61 of a housing 62. The control element 63 is surrounded by a luminous ring formed by the light-guiding element 64. Furthermore, a printed circuit board 65, to which a light-emitting diode 66 is applied, is arranged in the housing 62. The light-emitting diode 66 emits light in the direction of the front face 61. However, on account of the installation conditions, the said diode is arranged laterally offset with respect to the control element 63 in the printed circuit board 65. Light is coupled into the light-guiding element 64 via an arc segment 67. This structure results in the control unit having a relatively large physical depth.
EP 0 498 451 A1 discloses a motor vehicle indicating instrument which can be illuminated. An incompletely closed annulus is provided therein for the purpose of illuminating the indicating instrument, the light source being arranged in the missing part of said annulus. On account of the different installation conditions in the case of a relatively large indicating instrument in comparison with a relatively small control element, this solution cannot readily be applied to control elements. This is true particularly because the installation space directly behind the control element is not always available for fitting the light source.
An object of the invention, therefore, is to specify a control unit of a motor vehicle having control elements which can be illuminated, which control unit has a small installation depth and, at the same time, ensures homogeneous light distribution, in particular so-called xe2x80x9chot spotsxe2x80x9d, i.e. points of high luminance being avoided.
It will be understood by those skilled in the art that the reference to xe2x80x9cannularxe2x80x9d includes oval forms as well.
The 1st exemplary embodiment comprises a solution for illuminating an individual, in particular a round, control element. The control element can be illuminated via an annular optical waveguide which essentially encloses the control element in the control surface. According to the invention, the optical waveguide has a closed annular form, the optical waveguide having a tangential bulge which forms a light coupling-in area perpendicular to the annular light coupling-out area. A physical depth which is reduced compared with the known embodiments is obtained as a result of this configuration. Compared with the solution embodiment which is known from instrument illumination, the invention has the advantage that the light source can be arranged offset laterally with respect to the control element, or the indicating instrument in the known embodiment. Consequently, the installation space behind the control element can be fully utilized for the actual element to be controlled, e.g. a potentiometer. In particular, the light coupling-out area of the annular optical waveguide is arranged essentially in a positively locking manner in the visible surface of the control unit and encloses the control element. This results in the control unit having a largely flat front face from which merely the control element itself projects.
In order to achieve a targeted coupling of light into the optical waveguide without scattered light occurring to an unnecessary extent, provision is made, in particular, for a light source having a single, directed light coupling-out area to be used. This may involve, in particular, a light-emitting diode. In order also still to be able to arrange a printed circuit boardxe2x80x94on which the light-emitting diode is arrangedxe2x80x94essentially parallel to the housing front face of the control unit, it is furthermore provided that the single light exit area of the light source is arranged perpendicularly to an area of the light source with electrical contact elements which establish the connection to the printed circuit board.
In a 2nd embodiment of the invention, it is provided that a plurality of control elements can be illuminated via an optical waveguide. In this case, the optical waveguide has a plurality of light coupling-out areas which are arranged in the same plane and are arranged on finger-like extensions of an otherwise planar optical waveguide. In this case, the light coupling-out areas are arranged at right angles to a common light coupling-in area. A very small installation depth can once again be obtained with such an optical waveguide as well. In particular, in this case as well, a light source having a single, directed light coupling-out area is again used in order to keep the proportion of scattered light as low as possible. In particular, the light source may therefore be a light-emitting diode. In order to be able to arrange a printed circuit board in the customary manner parallel to the front face of the control unit in this embodiment as well, the light source being arranged on the printed circuit board, in this case as well it is provided, in particular, that the single light exit area of the light source is arranged perpendicularly to an area of the light source with electrical contact elements which establish the connection to the printed circuit board.